linux-kernel - Re: [PATCH 1/2] mm, printk: introduce new format string for flags

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Date:	Thu, 3 Dec 2015 17:04:30 -0800
From:	yalin wang <yalin.wang2010@...il.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Vlastimil Babka <vbabka@...e.cz>,
	"open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Minchan Kim <minchan@...nel.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>
Subject: Re: [PATCH 1/2] mm, printk: introduce new format string for flags


>> Technically, I think the answer is yes, at least in C99 (and I suppose
>> gcc would accept it in gnu89 mode as well).
>> 
>> printk("%pg\n", &(struct flag_printer){.flags = my_flags, .names = vmaflags_names});
>> 
>> Not tested, and I still don't think it would be particularly readable
>> even when macroized
>> 
>> printk("%pg\n", PRINTF_VMAFLAGS(my_flags));
> i test on gcc 4.9.3, it can work for this method,
> so the final solution like this:
> printk.h:
> struct flag_fmt_spec {
> 	unsigned long flag;
> 	struct trace_print_flags *flags;
> 	int array_size;
> 	char delimiter; }
> 
> #define FLAG_FORMAT(flag, flag_array, delimiter) (&(struct flag_ft_spec){ .flag = flag, .flags = flag_array, .array_size = ARRAY_SIZE(flag_array), .delimiter = delimiter})
> #define VMA_FLAG_FORMAT(flag)  FLAG_FORMAT(flag, vmaflags_names, ‘|’)
a little change:
	#define VMA_FLAG_FORMAT(vma)  FLAG_FORMAT(vma->vm_flags, vmaflags_names, ‘|’)


> source code:
> printk("%pg\n", VMA_FLAG_FORMAT(my_flags)); 
a little change:
	printk("%pg\n", VMA_FLAG_FORMAT(vma)); 

> 
> that’s all, see cpumask_pr_args(masks) macro,
> it also use macro and  %*pb  to print cpu mask .
> i think this method is not very complex to use .
> 
> search source code ,
> there is lots of printk to print flag into hex number :
> $ grep -n  -r 'printk.*flag.*%x’  .
> it will be great if this flag string print is generic.
> 
> Thanks

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